Many types of microelectronic devices or precursors of microelectronic devices are prepared by methods that include a “lapping” process, which is a step or series of steps of abrading a surface of the device or precursor (i.e., a “substrate”) to remove material from the surface. Material may be removed for one or more of: preparing a flat (planarized) surface; producing a desired feature height or “depth” at one area of the surface; producing a desired shape of the surface; or for a combination of these different purposes. The type of microelectronic device or precursor being processed will vary and may include devices and precursors such as integrated circuits, optical devices, and magnetic read and read-write heads that include a slider.
A specific example of a type of microelectronic device that is commonly prepared by steps that include lapping is a “slider assembly” (alternately referred to as a “head assembly”) for use in a hard disk drive system. Hard disk drive systems (HDDs) include one or more magnetic data storage disks. A transducing head carried by a slider assembly near the disk, while the disk spins, is used to read from or write to data tracks on the magnetic disk. The slider assembly includes a transducing read head, a transducing write head, or both, along with a “slider element” that includes a surface that faces the spinning disk and acts as an “air bearing” relative to the spinning disk. During use, the slider assembly is carried at a location very close to the spinning disk surface, but not in contact with the disk surface. The transducing (read or write) head must be suspended or “fly” over the spinning disk surface at a predetermined head-to-disk spacing. To maintain a consistent distance between the rotating disk and the head assembly, the surface of the slider element is shaped to create a layer of air in-between the rotating disk surface and the suspended head assembly. The layer of air produces an aerodynamic force against the head assembly so as to urge the head assembly away from the surface of the rotating disk. A load force provided by a flexure or spring that carries the head assembly opposes the aerodynamic force, and the resultant of the two opposing forces determines the flying height of the head assembly.
A slider assembly, including one or more transducing heads and the slider element, is typically produced by using thin film deposition techniques also used to produce many other microelectronic devices. In a typical process, an array of slider assemblies is formed on a common substrate or wafer. Each slider assembly contains at least one transducing head, as well as a slider element having a surface on one side of the slider assembly. After forming the wafer to contain a large number of slider assemblies, the wafer is sliced into a number of groups of connected slider assemblies for further processing. By some methods, rows or “bars” (“slider bars”) of slider assemblies are cut from the wafer, with each slider bar having a number (e.g., seventy) of slider assemblies connected in a side-by-side pattern on each bar.
Typically, the slider bars (containing multiple, connected slider assemblies) are processed by a lapping step. The lapping step processes the surfaces of the slider assemblies to remove a small or minute amount of material from each slider assembly surface to result in a desired thickness or depth (referred to as the “stripe height”) between that surface and one or more transducer heads of the slider assembly, which are located adjacent to and below that surface. Lapping is also performed and can be effective to remove material from the slider element of slider assemblies, to produce a desired surface shape.
To carry out the lapping process, a microelectronic device substrate (e.g., a slider bar) is secured to a carrier, and the carrier is used to hold a surface of the substrate against a moving abrasive material, with a light amount of pressure. Contacting the surface of the substrate with the abrasive material, with relative motion between the surface and the abrasive material, is effective to remove small or minute amounts of material from the surface of the substrate. A lubricant such as mineral oil is also normally present at the interface between the substrate surface and the moving abrasive material. The substrate is commonly secured to a surface of the carrier by a pressure-sensitive adhesive, which must exhibit certain specific performance requirements to be useful for this purpose, such as generally providing a secure engagement between a surface of substrate and a surface of the carrier, even in the presence of a lubricant.
Industry standard adhesives for securing a microelectronic device substrate to a carrier for a lapping step include silicone-based (polymeric silicone-based, e.g., polydimethylsiloxane) pressure-sensitive adhesives. But silicone-based adhesives have disadvantages in that they tend to swell or leach during processing, e.g., in the presence of certain lubricants used in lapping processes, which causes contamination of a substrate that is being processed by the lapping step, of the lapping equipment, or both. Silicone can be highly problematic if present as a contaminant of a microelectronic device, even if present at only a very tiny amount. Unlike organic contaminants, silicone cannot be oxidized by atomic oxygen. If oxidization of a silicone contaminant at a substrate surface is attempted, a glassy silicate, which is very difficult to remove, will be formed and will remain at the surface. Silicones, being useful as release agents, also cause great difficulties in trying to bond an applied layer of material to a surface that is contaminated with a silicone; as an example, if metallization is attempted on a surface that is contaminated with silicone, adhesion is greatly diminished. Silicone contamination of magnetic and chemical sensors can be highly problematic; even parts-per-million amounts of silicone present on a surface of a sensor can dramatically and quickly impede performance of the sensor. Minimal exposure of a hard disk read-write head to silicone can result in errors or drive failure.
As a general matter, an improvement in any aspect of the various processes used to produce microelectronic devices will always be desired. With more specific regard to lapping steps, the Applicant has now discovered that certain types of non-silicone-based pressure-sensitive adhesives can be successfully used to secure a microelectronic device substrate to a carrier, with useful or advantageous results. This discovery will allow for the elimination of the negative effects that result from using standard silicone-based adhesives in lapping steps.